1. Field of Invention
The invention relates to a phase detection method and its device and, in particular, to a phase detection method and its device used in phase modulation systems.
2. Related Art
In normal communications technologies, applications of phase demodulator are very common. They are often installed in phase modulation systems to convert a high-frequency signal into a digital signal. A conventional phase demodulator is shown in FIG. 1, containing a phase demodulator 6 of a symbol timing recovery circuit 65. As shown in the drawing, the phase demodulator 6 further includes a radio circuit 61, an A/D (Analog/Digital) converter 62, a matched filter 63, and a phase difference generating circuit 64.
The radio frequency circuit 61 receives an analog high-frequency signal and converts it into an analog intermediate-frequency (IF) signal. The analog IF signal is then converted by the A/D converter 62 and filtered by the matching filter 63 to generate an in-phase signal I and a quadrature signal Q. Generally speaking, the in-phase signal I and the quadrature signal Q are signed digital signals. The phase difference generating circuit 64 makes computations to obtain a phase difference from the in-phase signal I and the quadrature signal Q. The symbol timing recovery circuit 65 performs symbol timing recovery according to the phase difference output from the phase difference generating circuit 64.
The phase difference generating circuit 64 generally contains a phase detecting unit 641 and a phase difference generating unit 642 (FIG. 2). The phase detecting unit 641 determines a phase 0 according to the in-phase signal I and the quadrature signal Q. More concretely speaking, the phase detecting unit 641 usually uses a look-up table to determine the phase xcex8. The phase difference generating unit 642 uses the phase xcex8 to obtain a phase difference xcex94xcex8 for the symbol timing recovery circuit 65.
As described before, the phase detecting unit 641 of the phase difference generating circuit 64 obtain the phase xcex8 by consulting a look-up table, therefore the correspondence between the phase xcex8 and the signals I and Q have to be stored in a look-up table in the memory of a phase modulation system in advance. However, the correspondence look-up table of the xcex8 and the signals I and Q normally occupies a lot of the memory so that the demodulator has more gate counts during the ASIC process. This is very inconvenient for communications devices with little memory (such as mobile phones) because the look-up table, thus lowering the efficiency of the memory, occupies a large portion of the memory. How to use other methods to obtain the phase without employing a large look-up table so that the demodulator can minimize its memory uses has become an important subject of the field.
In view of the foregoing problems, it is then an objective of the invention to provide a phase detection method and its device that can save a large amount of memory space.
The featured technique of the invention is to use an orthogonal coordinate system and a polar coordinate system to obtain the phase. Using the disclosed method, it is not necessary to employ a table to obtain the phase, thus saving a lot of memory space.
To achieve the above objective, the invention provides a phase detection device, which contains a quadrant determining module, a first comparison module, a second comparison module, a coordinate transforming module, and a phase computing module. The quadrant determining module and the first comparison module are used to obtain a first and a second phase approximate values. The second comparison module and the coordinate transforming module are used to obtain a third phase approximate value, with which the phase computing module calculates a total phase.
In addition, the invention also provides a phase detection method including a quadrant determining procedure, a first comparison procedure, a second comparison procedure, a coordinate transforming procedure, and a phase computing procedure. The quadrant determining procedure and the first comparison procedure obtain a first and a second phase approximate values. The second comparison procedure and the coordinate transforming procedure are used to obtain a third phase approximate value, with which the phase computing procedure calculates a total phase.